A hybrid vehicle has electric power components, such as motors, alternators, electric actuators and batteries, powered by high-voltage, high-amp alternating or direct current; and a low-voltage/low-amp electric circuit for controlling the electric power components and any other controls or servocontrols.
The high voltage and amperage of the electric power components may interfere with the low-voltage electric circuit signals, thus impairing reliability of the vehicle and, in particular, altering the control signal from the user or the central control unit and so resulting in uncommanded, unpredictable operation of the vehicle
Hybrid vehicles at least partly solve the low-efficiency, high-noise problems typical of internal combustion engine work vehicles, including telescopic-arm lift vehicles.
In conventional non-hybrid vehicles, the internal combustion engine must be kept running continuously. To drive the vehicle, which is normally a four-wheel drive, power is transferred from the internal combustion engine to a hydraulic motor; and, to run the hydraulic lift system, power is transferred from the internal combustion engine to a hydraulic pump via a mechanical drive. The internal combustion engine is thus run continuously, to move the vehicle forward and in reverse, as well as to operate the lift system, which is normally controlled by hydraulic actuators operated by the hydraulic pump, in turn operated by the internal combustion engine via a drive.
The above features and drawbacks apply to most work and farm vehicles.
In the case of telescopic-arm vehicles, the telescopic arm is normally controlled by an actuator powered by a hydraulic pump. For layout reasons, as described for example in U.S. Pat. No. 5,707,202, the internal combustion engine is housed in a side compartment between the two vehicle axles, and which houses a number of components, a compressor, a filter, and a hydraulic valve assembly. The vehicle is normally driven by a hydraulic (hydrostatic) motor controlled by the internal combustion engine operated at various speeds by the user. A change in the speed of the internal combustion engine changes the travelling speed of the vehicle and/or generates power/torque to operate the telescopic arm.
In recent years, numerous patent applications have been filed with the object of reducing vehicle consumption and acoustic and pollutant emissions.
Numerous listings relate to hybrid vehicles comprising electric machines.
From a layout standpoint, documented hybrid vehicles can be classified as: series, parallel, and power-split parallel.
Hereinafter, the term ‘input’ refers to the primary, normally internal combustion (diesel), engine; ‘output’ to the vehicle drive axles; M/G1 to a first electric motor/generator; and M/G2 to a second electric motor/generator.
In the series solution, the input internal combustion engine is connected mechanically to electric motor/generator M/G1 to produce and supply the batteries with electric power, which is used, when needed, by electric motor/generator M/G2 to drive the output. In which case, the vehicle is driven fully electrically.
In the parallel solution, the input internal combustion engine is connected mechanically by an epicyclic reducer to electric motor/generator M/G1 and to electric motor/generator M/G2 to drive the output. And various mechanical drive layout and control solutions permit combined electric-diesel drive of the vehicle.
The series-parallel (input-split or output-split) hybrid configuration has two main power paths: a mechanical path, along which the power generated by the internal combustion engine is transmitted directly to the wheels; and an electrical path, along which the power generated by the internal combustion engine is first converted to electric power by the generator, and then converted back to mechanical power and transmitted to the wheels or also to any other systems, such as the hydraulic pump, e.g. to operate the telescopic arm.
One example of a hybrid drive with different parallel solutions is described in Patent US2002091028.
US2005061564 describes a parallel, input-split/output-split layout, which has the drawback of being fairly complicated mechanically and in terms of overall vehicle control. Especially in the case of hybrid work vehicles involving high power levels, the hydraulic system, which normally demands more or less the same amount of power as for driving the vehicle, would further complicate the drive, the configuration of which is thus less than optimum.
Because of functional and layout restrictions and the technical choices involved, the known art therefore tends to privilege partial solutions aimed at resolving a specific problem, as opposed to optimizing the vehicle as a whole.
Patent Application EP-A-1914101 describes a hybrid vehicle which, by means of a power splitter, allows part of the power from the diesel engine to be used partly to power the hydraulic system, and partly to charge the batteries by means of a generator; and the power stored in the batteries is given back when needed. There being no clutches, however, the diesel engine has to be kept running continuously.
US20090199553 describes a hybrid excavator, in which the mechanical power generated by the diesel engine is converted by a reversible generator to electric power, which is then used by the same reversible generator to power a hydraulic pump to operate the arm and hydraulic systems. Again, however, there being no clutches, the diesel engine has to be kept running continuously.
JP-A-2005133319 describes a hybrid vehicle operating layout, in which the internal combustion engine and electric motor are located at the rear with the batteries. This is a particularly bulky configuration, which, by raising the centre of gravity, is unsuitable for telescopic-arm vehicles, which, for reasons of stability, have to maintain a low centre of gravity to avoid rolling over. Moreover, no mention is made of the problems involved in assembling individual components to minimize the impact on the layout of a telescopic-arm vehicle.
The hybrid operating solution described allows the internal combustion engine to be run connected to a generator, which powers a battery pack and, from this, an electric motor to drive the vehicle.
More specifically, the internal combustion engine and electric motor are user-controlled directly by first pedal, which controls both the internal combustion engine and the electric motor, and a second pedal, which only controls the electric motor. Which means the user can also act on the speed of the internal combustion engine on the basis of the load demanded of the electric motor, at the expense of the energy efficiency of the vehicle as a whole.
Moreover, unlike other types of vehicles, such as telescopic-arm vehicles, the vehicle described is one of a category of excavators which require more, or at least the same amount of, power to operate the shovel than to drive the vehicle.
This greatly affects the size of hybrid excavator battery packs. In fact, an excavator of the type described in JP-A-2005133319 would need batteries of several hundred kWh to operate one hour with the electric vehicle drive motor and the shovel powered fully electrically, i.e. with the internal combustion engine off. So the batteries would be of such bulk and weight as to be unmountable on the excavator as shown.
The excavator described therefore cannot be run fully electrically to simultaneously drive the vehicle and operate the shovel. On the contrary, the internal combustion engine must be run continuously to simultaneously operate the hydraulic system and drive the vehicle; and the hydraulic system can only be powered electrically when the vehicle is stationary.
The system proposed in JP-A-2005133319 therefore basically amounts to saving power by turning the internal combustion engine off when the vehicle is stationary, and using the power of the batteries and the reversibility of the electric machine to run the hydraulic systems with no emissions and for short periods of time when the vehicle is stationary. No mention is made of the need to balance and control power demand in different vehicle operating conditions, in terms of battery pack sizing and power distribution between vehicle drive and hydraulic system operation.
As stated, the known art thus tends to privilege partial solutions aimed at resolving specific problems, as opposed to achieving an overall solution covering the vehicle as a whole. Another important point to note is the stress future regulations are expected to place on energy-saving and noise-reducing performance.